1. Field of the Invention
The present invention relates to vertically mountable, bare or minimally packaged semiconductor dice. In particular, this invention relates to semiconductor dice having bond pads on an edge thereof. More particularly, a preferred semiconductor device according to the present invention has all of its bond pads distributed along a single edge thereof. In use, upon vertical orientation and alignment of the semiconductor device upon a carrier substrate, an electrically conductive material establishes an electrical connection between each bond pad and a corresponding terminal of the carrier substrate.
2. State of the Art
The direct attachment of a semiconductor device to a circuit board is known in the art as chip-on-board technology. Semiconductor dice that are directly mountable to a circuit board typically include bond pads adjacent more than one edge thereof or in an area array over the active surface thereof. Methods for attaching dice directly to a circuit board include flip-chip technology and tape automated bonding. Typically, when such techniques are employed, a semiconductor device which includes bond pads on the active surface thereof is oriented over the circuit board and substantially parallel thereto so that an electrical connection will be established between the semiconductor device and the circuit board. After connecting such a semiconductor device to a circuit board, a protective coating may be applied over the semiconductor device.
However, the placement of a semiconductor device directly against a circuit board is somewhat undesirable in that, due to the parallel orientation of the semiconductor device relative to the circuit board, and the typical placement of the semiconductor device""s active surface against the circuit board, the heat must pass through both the circuit board and the semiconductor device in order to transfer away from the semiconductor device. Thus, the transfer of heat away from the semiconductor device is relatively slow. The horizontal orientation of the semiconductor device also consumes a great deal of area or xe2x80x9creal estatexe2x80x9d on the circuit board. Moreover, chip-on-board attachments are typically permanent, making them somewhat undesirable from the standpoint that they are not readily user-upgradeable.
Vertical surface mount packages are also known in the art. When compared with traditional, horizontally mountable semiconductor packages and chip-on-board devices, many vertical surface mount packages have a superior ability to transfer heat away from the semiconductor device. Vertical surface mount packages also consume less area on a circuit board than a horizontally mounted package of the same size. Thus, many skilled individuals in the semiconductor industry are finding vertical surface mount packages more desirable than their traditional, horizontally mountable counterparts.
The following United States Patents disclose various exemplary vertical surface mount packages: U.S. Pat. No. Re. 34,794, issued to Warren M. Farnworth on Nov. 22, 1994; U.S. Pat. No. 5,444,304, issued to Kouija Hara and Jun Tanabe on Aug. 22, 1995; U.S. Pat. No. 5,450,289, issued to Yooung D. Kweon and Min C. An on Sep. 12, 1995; U.S. Pat. No. 5,451,815, issued to Norio Taniguchi et al. on Sep. 19, 1995; U.S. Pat. No. 5,592,019, issued to Tetsuya Ueda et al. on Jan. 7, 1997; and U.S. Pat. No. 5,635,760, issued to Toru Ishikawa on Jun. 3, 1997.
Many vertical surface mount packages are somewhat undesirable in that they include leads which operatively connect a semiconductor device to a circuit board. The leads of such vertical surface mount packages tend to increase the impedance and decrease the overall speed with which the semiconductor device conducts electrical signals. Moreover, the packaging of many such vertical surface mount packages adds to their undesirability. Typically, packaging requires multiple additional manufacturing steps, which translates into increased production costs. The packaging of many vertical surface mount packages also tends to consume a substantial amount of area on the circuit board. Moreover, many vertical surface mount packages are not user-upgradeable.
Some electronic devices have electrical contacts disposed on the edges thereof. Typically, such contacts are formed by drilling a hole through the substrate. The hole, or at least the perimeter thereof, is then filled with an electrically conductive material. Solders, molten metals and other electrically conductive materials are useful for filling the holes and forming the electrical contacts. When the substrate is separated into distinct boards or dice, the contacts are divided such that they are located on the edge of the distinct boards or dice. Such devices are illustrated and described in the following United States patents: U.S. Pat. No. 5,266,833 (the xe2x80x9c""833 patentxe2x80x9d), issued to David F. Capps on Nov. 30, 1993; U.S. Pat. No. 5,471,368 (the xe2x80x9c""368 patentxe2x80x9d), issued to Alan P. Downie et al. on Nov. 28, 1995; and U.S. Pat. No. 5,635,670 (the xe2x80x9c""670 patentxe2x80x9d), issued to Kenji Kubota et al. on Jun. 3, 1997.
The ""833 patent also describes semiconductor dice having bond pads on the edges thereof. Such bond pads are formed by disposing a grid of xe2x80x9cthin electrically conductive wires 14 formed of a suitable electrical conductive material, such as copper or gold, . . . in a semiconductor material during the growth of a semiconductor crystal 16.xe2x80x9d (Col. 4, lines 32-36.)
In order to achieve appropriate bond pad placement, great consistency and accuracy are required in the orientation of the conductive wires during formation of the silicon ingot, singulation of the wafer, and fabrication of circuit traces on each semiconductor device. However, because the silicon is transferred after being sawed into wafers, it is somewhat difficult to maintain such consistency and accuracy in the placement of the wires. Further, such a method of forming edge-bound bond pads does not permit varying the bond pad placement on different wafers cut from the same ingot. U.S. Pat. No. 5,668,409 (the xe2x80x9c""409 patentxe2x80x9d), issued to Stephen Joseph Gaul on Sep. 16, 1997, discloses a vertically mountable, bare semiconductor die which includes bond pads along the edge thereof. The ""409 patent discloses vertical mounting of that device to a circuit board by solder reflow techniques. However, that device is somewhat undesirable in that fabrication thereof requires several additional steps relative to the fabrication of typical chip-on-board semiconductor devices. The requirement of additional fabrication steps and the related requirement of additional fabrication materials increase the manufacturing cost of such semiconductor devices. Moreover, the disclosed use of solder reflow techniques to attach the semiconductor device of the ""409 patent to a circuit board prohibits users from readily upgrading or otherwise replacing that semiconductor device.
Thus, a vertically mountable bare semiconductor device is needed which has reduced impedance relative to devices in the prior art, has good thermal conductivity, consumes less area or xe2x80x9creal estatexe2x80x9d on a circuit board, and is user-upgradeable. A method of fabricating a semiconductor device with bond pads in select positions on the edges thereof with fewer steps is needed. A method of directly mounting an edge-bumped semiconductor device perpendicularly relative to a carrier substrate is also needed.
The vertically mountable, edge-bumped semiconductor device of the present invention addresses each of the foregoing needs.
The semiconductor device of the present invention includes bond pads disposed on the edges thereof. More preferable, the bond pads are disposed on a single edge of the semiconductor device. Placement of the bond pads on an edge of the semiconductor device facilitates direct vertical mounting of the semiconductor device to a carrier substrate. Thus, when such a semiconductor device is mounted perpendicularly relative to a carrier substrate, packaging and leads are not necessary to establish an electrical connection between the bond pads and the corresponding terminals on the carrier substrate. The direct connection between the bond pads of the semiconductor device and carrier substrate terminals also imparts the semiconductor device of the present invention with low impedance.
A fabrication method according to the present invention includes creating notches in a semiconductor wafer in locations where bond pads are desired and redirecting a circuit trace into selected notches. A protective overcoat may also be formed over the active surfaces of the dice. The metalized notches may be filled with a solder ball, other metal member or other electrically conductive material. The wafer is singulated along each of the metalized notches to form bond pads on the edges of each resultant semiconductor device.
An alignment device, which attaches the semiconductor device to a carrier substrate, includes a body which defines at least one slot therein, into which a semiconductor device is insertable. The alignment device may also include a mechanism for biasing the semiconductor device against a carrier substrate. Preferably, each slot is wider at its top opening than at its bottom opening, which abuts the carrier substrate, in order to facilitate insertion of a semiconductor device therein. The mechanism for biasing establishes and maintains electrical contact between the bond pads of the semiconductor device and the corresponding contacts of the carrier substrate.
Other advantages of the present invention will become apparent through a consideration of the appended drawings and the ensuing description.